It is well known to employ ultraviolet (UV) light in the field of photography in order to image objects that react by fluorescing at specific wavelengths in the UV spectrum. Typically, these light sources are mercury vapor lamps, due to their strong emission peaks in the UV region. In order to increase signal to noise ratio of the fluorescence signal, a standard UV band pass filter is placed in front of the light source, allowing only the desired wavelength (e.g., the λ max absorption for fluorescence) of light to pass, reducing the effective output energy of the lamp significantly. This type of photographic arrangement often requires long exposure times, in excess of 5 seconds, making digital photography impractical, and further requires a photographic field which is maintained in the absence of ambient visible light. These limitations severely restrict the photographer in the type of camera that can be employed and location(s) he or she can operate within.
A popular method of imaging fingerprints on non porous items is as follows:
The object is placed in an air tight container, preferably a vacuum chamber, along with a small container containing cyanoacrylate (super glue), the cyanoacrylate is heated until it starts to out-gas, and the resulting fumes attach to the oil left on the object by the fingerprint. Some prints will be visible to the unaided eye with this method, however faint or very light prints require a second step. The second step is to treat the object with the fumed prints to a coating of Basic yellow 40. Basic yellow 40 is a textile dye that is used to stain cyanoacrylate treated fingerprints on non-porous surfaces. The dye is also known as Maxillon Brilliant Flavine, Brilliant Yellow and Panacryl Brilliant Yellow. Stained fingerprints appear yellow when viewed under blue (450 nm) light sources. The object is then viewed under illumination of a 450 nm light source, through a KV 550 nm viewing filter.
Typical crime scene and laboratory ultra violet light sources direct a full spectrum light through a fiber optic conduit of quartz glass or a liquid light guide, and utilize a variety of interchangeable band pass filters between the light source and the light guide's input or common end. This permits only a relatively small field of illumination from a light guide of 0.5 inch diameter, and is designed primarily for observation.
The individual prints are selected, then composed and focused on, through the camera.
The exposures are long, for example 5 seconds to 15 minutes, based on the amount of dye fluorescence, which is in turn dependent on the intensity of blue or UV light. To maximize the effect the area needs to be very dark, and using UV light for illumination limits visible interference.
Repetitive pulse operation of xenon light sources is known, for example as stroboscopes, red-eye reduction preflash, sterilization, and for other illumination purposes.
See www.xenon-corp.com/sterilization.html, www.chem.helsinki.fi/˜toomas/photo/flash.html;
www.chem.helsinki.fi/˜toomas/photo/flash-discharge.html; www.chem.helsinki.fi/˜toomas/photo/flash-discharge/redwait.html; www.chem.helsinki.fi/˜toomas/photo/flash-discharge/setup.html; www.chem.helsinki.fi/˜toomas/photo/flash-discharge/regular.html; www.chem.helsinki.fi/˜toomas/photo/flash-discharge/hispeed.html; members.misty.com/don/samflash.html; and www.photozone.de/3Technology/flashtec5.htm, each of which is expressly incorporated herein by reference in its entirety.